1. Field of the Invention
The present invention relates to ball-and-socket prosthetic hip joints, which include an acetabular cup positioned within a patient""s acetabulum to serve as the socket for the hip joint, and more particularly, to a method and apparatus for removing the acetabular cup from the acetabulum.
2. Description of the Related Art
Prosthetic ball-and-socket hip joints generally include a femoral component and an acetabular component, the acetabular component including an acetabular cup positioned in a patient""s acetabulum which serves as the xe2x80x9csocketxe2x80x9d for the hip joint. The acetabular cup is typically made of stainless steel or titanium, having a hemispherical outer surface which can be roughened to allow the acetabular bone to grow therein to anchor the acetabular cup within the acetabulum. Additionally, a liner of suitable material, such as ultra-high molecular weight polyethylene (UHMWPE) for example, is received within the acetabular cup, and includes a hemispherical recess for receiving the ball end of the femoral component of the prosthetic hip joint.
During a prosthetic hip joint revision procedure, the acetabular cup is removed from the acetabulum and replaced with a new acetabular cup. To remove the acetabular cup, a chisel-like osteotome is used, which includes a blade for cutting through the acetabular bone surrounding the hemispherical outer surface of the acetabular cup, and a head which may be struck by a mallet to drive the blade through the bone adjacent the acetabulum. In use, the blade of the osteotome is positioned near the acetabular cup, and the head of the osteotome is struck with the mallet to make a cut in the bone adjacent the acetabular cavity near the acetabular cup. Thereafter, the osteotome is withdrawn and repositioned, and the procedure is repeated until sufficient cuts have been made around the acetabular cup to permit removal thereof from the acetabulum. Thereafter, a new acetabular cup is positioned within the acetabulum.
What is needed is an improved apparatus and method for quickly and easily removing an acetabular cup from an acetabulum with minimal loss of acetabular bone, while preserving a relatively intact, hemispherical acetabular recess into which a new acetabular cup may be fitted.
The present invention provides an improved method and apparatus for removing an acetabular cup from an acetabulum. A surgical kit includes an osteotome instrument having an elongated handle shaft terminating in a head portion, and a plurality of interchangeable osteotomes and pivot elements, such as spherical heads, which may be attached to the head portion of the instrument. Each spherical head is sized to be received within the recess of an acetabular cup liner of a corresponding size, and at least two osteotomes, having curved blades of different lengths, are sized for use with acetabular cups of different sizes. When a corresponding spherical head and osteotome are attached to the instrument, the spacing between the osteotome blade and center of the spherical head corresponds to the spacing between the center of the recess in the acetabular cup liner and the rim of the acetabular cup. The blade of each osteotome is curved to generally match the curvature of the outer hemispherical surface of the acetabular cup.
In use, the spherical head of the instrument is seated within the recess of the acetabular cup liner such that the end of the osteotome blade is disposed closely adjacent the rim of the acetabular cup. In this manner, the position of the blade is fixed relative to the rim of the acetabular cup due to the seating of the spherical head within the recess of the acetabular cup liner and the spacing between the osteotome blade and the spherical head. Thereafter, the handle shaft of the instrument may be pivoted and/or rotated to make several cuts with the curved osteotome blade which are closely adjacent the outer hemispherical surface of the acetabular cup, until the acetabular cup may be removed from the acetabulum.
In one embodiment of the present method, a first osteotome having a short blade may be used to cut around the outer hemispherical surface of the acetabular cup to a first depth. Thereafter, the first osteotome is removed from the instrument, and a second osteotome having a longer blade is attached thereto. The second osteotome is then used to cut around the outer hemispherical surface of the acetabular cup to the apex thereof, after which the acetabular cup may be removed.
Each osteotome blade may include a cutting surface along the end thereof for cutting acetabular bone in an arc from the rim of the acetabular cup toward the apex thereof, as well as a pair of side cutting surfaces for cutting in an orbital manner about the acetabular cup.
The handle shaft of the instrument may include a radially projecting handle lever to facilitate rotation of the instrument, and an impaction head at a proximal end of the handle shaft which may be struck by a mallet as necessary to drive the osteotome blade.
Advantageously, the seating of the spherical head of the instrument within the recess of the acetabular cup liner centers the instrument with respect to the acetabular cup, with the osteotome blade spaced a fixed distance from the spherical head and closely adjacent the outer hemispherical surface of the acetabular cup. Thus, the osteotome blade is guided during cutting by the spherical head to cut closely adjacent the acetabular cup such that loss of acetabular bone is minimized, and an intact, hemispherically-shaped acetabular recess remains after removal of the acetabular cup into which a new acetabular cup may be fitted.
Additionally, removal of an acetabular cup using the present instrument and method requires much less time than acetabular cup removal using prior osteotomes, thereby shortening the length of a prosthetic hip joint revision procedure.
In one form thereof, the present invention provides an apparatus for removing an acetabular cup from an acetabulum, the apparatus including a handle; a pivot element connected to the handle, the pivot element dimensioned to be received within an acetabular cup; and a blade connected to the handle and spaced from the pivot element, such that when the pivot element is received within the acetabluar cup, the blade is disposed externally of the acetabular cup closely adjacent an outer surface of the acetabular cup.
In another form thereof, the present invention provides a kit for removing an acetabular cup from an acetabulum, including an osteotome instrument; a spherical head removably mountable to the instrument, the spherical head sized to be received within an acetabular cup; and a blade removably mountable to the instrument.
In another form thereof, the present invention provides a method for removing an acetabular cup from an acetabulum, the acetabular cup having an outer surface, the method including the steps of providing an instrument including a spherical head and a blade, the spherical head and the blade spaced from one another; seating the spherical head within the acetabular cup; moving the instrument to make a series of cuts with the blade which are closely adjacent the outer surface of the acetabular cup; and removing the acetabular cup from the acetabulum.